A vehicle air bag module is a complete unit which is assembled apart from the vehicle and then coupled as a unit to the vehicle. Typically, an air bag module includes (i) a receptacle, (ii) an inflator and a folded air bag disposed in the receptacle, and (iii) a cover attached to the receptacle to complete an enclosure for the inflator and folded air bag. When the air bag module is coupled to a vehicle, the receptacle acts as a reaction device which transmits reaction forces to the vehicle structure. The cover forms a part of the vehicle dashboard or steering wheel cover.
When coupled to a vehicle, an air bag module operates to deploy the air bag at the onset of a vehicle collision. Specifically, at the onset of a collision, the inflator generates or releases large quantities of gas under relatively high pressure. The gas deploys the air bag by forcing the air bag out of the receptacle and inflating the air bag.
The cover of the module must be incorporated into the module in such a way that the cover does not impede the rapid and efficient deployment of the air bag. Specifically, the cover must be adapted either to separate from the receptacle or to rupture so as to enable the air bag to inflate outward from the receptacle. However, the cover should also be designed so that it does not fly away from the module unrestrained or fracture into pieces which fly away from the module unrestrained.
One known technique for incorporating a cover into an air bag module is to fasten the edge of the cover directly to the receptacle. The center of the cover is weakened so that the cover separates under pressure to permit the outward deployment of an air bag. However, the edge of the cover is intended to remain fastened to the receptacle, to prevent the segments of the cover from flying away from the receptacle. Examples of such a technique are disclosed in U.S. Pat. Nos. 4,810,005 to Fohl and 3,938,826 to Giorgini, et al.
Another known technique for incorporating a cover into an air bag module is to attach the cover directly to the surface of the air bag in such a way that the cover is effectively an integral part of the air bag. With such a technique, the entire cover separates from the receptacle along with the air bag. Examples of such a technique are disclosed in U.S. Pat. Nos. 3,945,665 to Tsutsumi, et al. and 3,624,810 to Hass. In each of these patents, the edge of the cover is sewn to the air bag, so that the cover effectively becomes part of the air bag. Expansion of the air bag material, however, can apply significant stresses to the entire cover and especially to the stitching that attaches the edge of the cover to the air bag. The cover and the stitching have to be designed to resist fracture of the cover and separation of the cover from the air bag under such expansion stresses.
Still another known technique for incorporating an air bag cover into an air bag module is a tether connected between the cover and the receptacle. U.S. Pat. Nos. 3,944,250 to Wulf, et al. and 3,968,979 to Schiesterl disclose such a technique. The Wulf, et al. patent shows a fabric band fastened at one end to a receptacle and at an opposite end to a cover. The Schiesterl patent discloses an elastic strip fastened to a cover and to a receptacle. Both patents use fasteners such as screws or rivets to secure the elastic strip or band to the receptacle. During deployment of the air bag, the cover separates as a unit from the receptacle. The tether is designed to maintain the cover connected to the receptacle. However, the tether appears to permit a fairly extensive range of movement of the cover as it separates from the receptacle.
Accordingly, applicants believe there is a need for new and useful ways to incorporate a cover into a vehicle air bag module to minimize further the possibility of the cover fracturing or flying away from the receptacle in an unrestrained manner during deployment of the vehicle air bag.
Moreover, applicants believe that to meet the growing demand for air bag modules, there is a continuing need to provide module structures which can be produced by mass production techniques.